Sensor for liquid and/or gas analysis directly connectable to a higher-ranking control system

ABSTRACT

A sensor of the type for liquid and/or gas analysis, which is connected to a measuring and/or evaluating system or, respectively, to a higher-ranking control system and has a sensor housing. The circuit for the collecting, processing and transmitting measured values to the measuring and/or evaluating system or to the control system ( 19 ) are provided in the sensor housing ( 2 ). This circuit has analog sensor electronics ( 3 ), an analog-digital converter ( 14 ) for converting the detected analog measured values into digital measured values, a processing unit ( 15 ) and communication device ( 17 ) for processing and transmitting the digital measured values to the measuring and/or evaluating system or to the control system ( 19 ) according to a standard communication protocol of process technology.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of commonly owned, co-pending U.S.patent application Ser. No. 13/182,602, filed Jul. 14, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sensor for liquid and/or gas analysis, whichis connected to a measuring and/or evaluating system or, respectively,to a higher ranking control system and which has a sensor housing.

2. Description of Related Art

Sensors of the type described above are known in different forms fromthe prior art. A liquid sensor having a sensor housing is thus knownfrom PCT Patent Application Publication WO 2005/031339 and correspondingU.S. Pat. No. 7,587,953 that is connected in a contact-free manner via acoupling to a transducer and further to a measuring and/or evaluatingsystem. A receiving sensor for collecting measured values, apre-processing unit for pre-processing the collected values, ananalog-digital converter for converting the collected analog measuredvalues into digital measured values and means (modem, power supply unit,inductor or radio module) for contact-free transmission of the digitalmeasured values to the transducer are located in the sensor housing. Thecoupling has means (inductor or radio module, amplifier, modem) forreceiving the contact-free transmitted digital measured values and aninterface for transmitting the measured values to the transducer. Thecontact-free transmission of the measured values between the sensor andthe coupling serves, in particular, the galvanic de-coupling of thesensor from the measuring and/or evaluating system.

Liquid and/or gas sensors have a relatively short operating life andthus have to be regularly exchanged. For economic reasons, it has beenattempted in previous years to relocate as much of the electronics aspossible from the sensor into the coupling. For this reason, thetransmitter part of the transducer is arranged in the coupling or isimplemented there, for example, by means of a processor or a computerprogram running on the processor in the known liquid and/or gas sensors.For economic reasons, the electronics are thus split into sensorelectronics, on the one hand, and cable-connection electronics, on theother hand, in which essentially the sensor signals are converted into aproprietary protocol in order to be able to then transmit them to themeasuring and/or evaluating system. The interface between the liquidand/or gas sensor and the cable (for example, via a coupling forcontact-free signal transmission) is costly and causes technicalproblems in respect to ambient conditions.

SUMMARY OF THE INVENTION

Based on the above described prior art, the object of the invention isto provide a sensor of the type in the introduction, which primarilymakes it possible to implement the entire system consisting of thesensor and the measuring and/or evaluating system or, respectively, thehigher-ranking control system in a more economical manner.

The sensor according to the invention, in which the object derived andshown above is met, is first and foremost characterized in that circuitmeans for the collecting, processing and transmitting measured values tothe measuring and/or evaluating system or, respectively, to the controlsystem are provided in the sensor housing, that the circuit meanscomprises analog sensor electronics, an analog-digital converter forconverting the detected analog measured values into digital measuredvalues, a processing unit and communication means for processing andtransmitting the digital measured values to the measuring and/orevaluating system or respectively, to the control system according to astandard communication protocol of process technology.

While in the type of prior art, to which the sensor and the measuringand/or evaluating system, or respectively, the higher-ranking controlsystem, the entire system as well as the above-described coupling andthe transducer belong, the sensor according to the invention is designedin such a manner that the coupling and a transducer subordinate to thecoupling are no longer necessary. This is made possible in that thesensor housing not only houses the analog sensor electronics, but ananalog-digital converter, a processing unit and communication means arealso provided for processing and transmitting the digital measuredvalues to the measuring and/or evaluating system, or respectively, tothe control system according to a standard communication protocol ofprocess technology.

The sensor according to the invention is intended for liquid and/or gasanalysis. This means that it can be designed for measuring the pH-value,the conductivity, the oxygen content, the chlorine content, the ozonecontent, the hydrogen peroxide content, the content of free chlorine,the content of residual chlorine, the turbidity and/or the solidscontent in the liquid or respectively, gas or as a photometer or as aspectrometer.

In the sensor according to the invention, the described circuit meansare preferably implemented at least partially as ASIC (applicationspecific integrated circuit).

The sensor according to the invention is preferably connected via a plugor in some other manner with detachable wiring to the measuring and/orevaluating system, or respectively, to the control system. A PLC(programmable logic controller), a control system that controls orregulates the process to be controlled or regulated cyclically, or anasset management system for anti-cyclical tasks in the process to becontrolled or regulated, e.g., for diagnostic tasks (advanceddiagnostics), the setting of parameters, determining the point in timeof necessary cleaning or calibration can also belong to the controlsystem. The sensor can either be directly or indirectly, for example viaa segment coupler, connected to the control system.

In the sensor according to the invention, the circuit means provided inthe sensor housing can be galvanically connected to one another.However, it is also possible to provide a galvanic separation, namelybetween the analog-digital converter and the processing unit and/orbetween the processing unit and the communication means. The galvanicseparation can, for example, be implemented in that a transformer isprovided as part of the electrical circuit in the sensor housing, viawhich an inductive transmission can occur on its primary inductor, onthe one hand and on its secondary inductor, on the other hand. Thegalvanic separation can, however, also be opto-electronic.

As described, the communication means for processing and transmittingthe digital measured values to the measuring and/or evaluating system,or respectively, the control system belong to the sensor according tothe invention, namely according to a standard communication protocol ofprocess technology. This, of course, can be carried out in differentmanners. On the one hand, the communication means can transmit thedigital measured values according to one of the following describedfield bus communication protocols to the control system: HART, ProfibusPA, Profibus DB, Foundation Field Bus in 2-wire technology. On the otherhand, however, there is the possibility of implementing thecommunication between the communication means and the measuring and/orevaluating system or, respectively, the control system via a wirelessinterface, in particular according to the wireless HART, WLAN, ZigBee orRFID standard.

A field bus joins field devices in one system such as sensing elements(sensors) and actuating elements (actuator) for means of communicationwith a measuring and/or evaluating system or, respectively, with acontrol system. When multiple communication members send their messageswith the same wire, then it has to be specified who (identification),what (measured value, command) and when (initiative) “has the say”.There are standard protocols for this. Field bus technology wasdeveloped in the 1980s in order to replace the parallel wiring of binarysignals that was common up to that point as well as the analogtransmission of signals with digital transmission technology. Today,there are many different field bus systems with different featuresestablished on the market. Field buses in the standard IEC 61158(“Digital data communication for measurement and control —field bus foruse in industrial control system”) have been standardized worldwidesince 1999. Multiple sensors and actuators are often required forcontrolling a system. Should the control occur electrically, thequestions arises how the sensors and actuators are to be joined to thecontrol device. Two basic variations are possible:

a) Parallel wiring—for each sensor and actuator, a cable is run from thecontrol device (control system, normally DCS (distributed controlsystem)).

b) Serial wiring—only one cable is run from the control device (DCS viaPLC); the cable is led past each sensor and actuator.

Due to the greater number of input and output points, the wiringcomplexity increases for parallel wiring with the increasing degree ofautomation in a system or machine. This is linked with complex projectplanning, installation, startup procedure and maintenance. Therequirements on the cables are often so high, e.g., that special cablesare installed for the transmission of analog values. In this manner,parallel wiring has become a serious cost and time factor in automationtechnology. In comparison, serial wiring of the components in the fieldsection by means of so-called field bus systems is significantly moreeconomical. The field bus replaces the parallel wires or, respectively,wire packages or cables or cable packages with one single bus cable andjoins all levels, from the field level to the control level. Regardlessof the type of automation device, for example, programmable logiccontrollers from different producers or PC-based controls, thetransmission medium of the field bus links all components together.These can be arbitrarily distributed in the field, since they are allconnected decentralized on-site.

The sensor according to the invention has been described essentially inrespect to its function or functions up to this point. However, theconstructive design can also be of importance. Insofar, a furtherteaching of the invention to that effect is that in the sensor accordingto the invention, the sensor housing is designed in the shape of ahollow cylinder and has a diameter of 12 mm. Additionally, in the sensoraccording to the invention, the sensor housing can consist preferably ofplastic, stainless steel, glass or ceramic.

In view of construction, a preferred design of the sensor according tothe invention is characterized in that the circuit means provided in thesensor housing are provided at least partially on a flexible printedcircuit board. Here, the printed circuit board can have multiple layers,preferably is designed as a sandwich panel.

The sensor according to the invention is preferably designed foroperational conditions of about +65° C. to +130° C. operationtemperature and about 6 to 8 bar operation pressure.

Additionally, the sensor according to the invention is, more exactly,the electronics provided in the sensor housing preferably have a modularconstruction. It is also possible, for example, to break down theelectronics into an analog module (sensor electronics), a digital module(calculating unit, computer) and a communication module (processing andtransmitting the digital measured values to the measuring and/orevaluating system or the control system). Preferably, the modules can becombined with one another in respect to different sensor systems andcommunication, so that the electronics for arbitrary types of sensors aswell as for arbitrary communications according to standard communicationprotocols of process technology can be compiled with existing modules.The modules can also be designed as FPGAs (field programmable gatearray) as direct input for an ASIC design. The digital module and/or thecommunication module can also be implemented as a one-chip solution,which allows for further miniaturizing the circuit inside of the sensorhousing. Different circuit parts can belong to the ASIC, for exampleflash memory, ROM, RAM, EEPROM, CPU, A-D converter, HART modem and/orcomponents belonging to a Profibus or a Foundation Field Bus.

As already stated, in view of construction, a preferred design of thesensor according to the invention is characterized in that the sensorhousing is designed in the shape of a hollow cylinder and has a diameterof 12 mm. This allows the sensor to be used in a standard installationnormally used in process technology and to be replaced easily andquickly. All of the process facilities (fittings, holders, etc.) arenormally designed for a sensor diameter of 12 mm, In some industries,e.g., wastewater and water industry, sensors are normal that havediameters of up to 45 mm, typically 25 mm and 45 mm, and in someexceptions even up to 100 mm. The sensors are typically 120 mm, 225 mmor even 420 mm long.

If, as is already described further above, the circuit means provided inthe sensor housing are at least partially provided on a flexible printedcircuit board, the limited space available inside of the sensor housingcan be particularly efficiently used. It is possible, for example thatthe flexible printed circuit board extends along the roundcross-sectional form of a long sensor housing having a hollowcylindrical shape.

If the particularly preferred design is implemented, in which theprinted circuit board has multiple layers, preferably designed as asandwich panel, different boards of the sandwich panel can begalvanically decoupled. A galvanic separation between the analog-digitalconverter and the communication means can be present in a one-boardsolution. The printed circuit board can be designed as a multi-layerboard, a 1- or 2-side board, a rigid/flexible board or a HDI-SBUmulti-layer board (HDI=high density interconnection, SBU=sequentialbuild-up).

In a particularly advantageous design, the sensor according to theinvention is designed for use in areas at risk of explosion and/or atrisk of fire damping. Here, the sensor meets the necessary requirementsfor an ATEX certification (ATEX=Atmosphere Explosible). These aredefined, for example, in the standard EN 50014 as well as in thestandard guidelines RiLi 94/9EG and RiLi 1999/92/EG. The compliance ofthe ATEX certification can be controlled by various certificationauthorities (PTB=Physikalisch-Technische Bundesanstalt, TÜV=TechnischerÜberwachungsverein, FM=Factory Mutual, CSA=Canadian StandardAssociation).

Finally, the sensor according to the invention can also be designed formeeting the requirements of SIL2. The sensor according to the inventionthen meets high requirements in operation safety (fail safe) and has aSIL2 certificate (SIL2=safety integrity level 2). Requirements for aSIL2 certificate are defined in the standards EN 61508 and EN 61511.

In detail, there are a number of possibilities for designing and furtherdeveloping the sensor according to the invention. Here, please refer tothe patent claims subordinate to patent claim 1 and to the followingdescription of a preferred embodiment in conjunction with the drawing.The drawing shows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a sensor known from the prior art and

FIG. 2 schematically depicts a preferred embodiment of a sensoraccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a known sensor 1 that has a sensor housing 2 that is madeof plastic or stainless steel. Sensor electronics 3 are provided insideof the sensor housing 2, which are designed and arranged to collectanalog measured values using the sensor 1. The sensor 1 is designed forliquid analysis, for example, for measuring the pH value, theconductivity, the oxygen content, the chlorine content, the ozonecontent, the hydrogen peroxide content, the content of free chlorine,the content of residual chlorine, the turbidity and/or the solids or gascontent in the liquid or is used as a photometer or as a spectrometer.

Of course, the sensor 1 can be used for gas analysis using a respectivedesign of the sensor electronics.

In the known sensor 1 shown in FIG. 1, a first processing unit isprovided in the form of a processor 4, which, inter alia, converts theanalog measured values into corresponding digital measured values. Theprocessor 4 does not have to be particularly productive, since itsessential task is to process the collected measured values forcontact-free transmission to a coupling element 5. In the shownembodiment, the wireless transmission to the coupling element 5 occursinductively. For this purpose, the sensor 1 also has a first inductance6. A further inductance 7 is provided in the coupling element 5. Asecond processing unit in the form of a processor 8, which processes thedigital measured values for transmission via a proprietary communicationprotocol, is subsequent to the inductance 7. The processed measuredvalues are transmitted to a communication controller 10 of a bus system11. The measured values are then transmitted via the bus system 11according to a proprietary communication protocol to a furthercommunication controller 13 assigned to a measuring and/or evaluatingsystem 12.

A transmitter, a measured value transducer and/or converter belong tothe measuring and/or evaluating system 12; it normally carries out allimportant calculations, e.g., signal main processing, samplerecognition, sensor diagnostic, noise suppression or reduction, sensorcalibration, filtering, feature extraction. The processed data are firsttransmitted to a higher-level control system 19 after the mainevaluation in the measuring and/or evaluating system 12. The measuringand/or evaluating system 12 is a relatively large box arranged outsideof the sensor 1. Data transmission between the measuring and/orevaluating system 12 and the control system 19 occurs via a bus system16 having communication controllers 17, 18 using typical transmissionprotocols from process technology (e.g., HART, Profibus PA, FoundationField Bus, etc.).

The control system 19 includes, for example, a programmable logiccontroller (PLC) or a so-called asset management system. The controlsystem 19 no longer carries out processing or manipulation of themeasured values, in particular, the control system 19 does not changethe measured values at all. Moreover, the control system 19 onlycollects the measured values and uses them, if necessary together withother measured values from other sensors or with saved information aboutthe process, for process control or process regulation, for example thecontrol of actuators, e.g., of valves, electromagnets or similarcomponents.

The known sensor has a relatively short lifespan, and thus, needs to bereplaced from time to time. The sensor 1 can be mechanically affixed inthe coupling element 5 and electrically and signally connected in orderto simplify replacement as well as to galvanically separate the sensorelectronics 3 from the measuring and/or evaluating system. Signaltransmission occurs contact-free via both inductances 6, 7. In thesensors 1 known from the prior art, it is attempted to shift as much ofthe electronics as possible from in the sensor housing 2 to the outside,e.g., into the coupling element 5 or the external measuring and/orevaluating system 12, in order to make the sensors 1 more economical.

In the sensor 1 according to the invention shown in FIG. 2, a verydifferent solution is chosen. Here, the goal is to integrate as much ofthe electronics as possible into the sensor 1. The sensor 1 according tothe invention 1 in FIG. 2 includes a sensor housing 2, in which thesensor electronics 3 are provided for collecting analog measured values.The sensor electronics 3 are designed essentially the same as in theknown sensors, e.g., as in sensor 1 in FIG. 1. The analog measuredvalues collected by the sensor electronics 3 are also converted intodigital measured values by an analog-digital converter 14 also providedin the sensor housing 2. These are then given to a calculating unit, forexample, in the form of a processing unit 15, which carries out apre-processing of the measured values and further processing for thetransmission to the external control system 19 according to a standardcommunication protocol of process technology via a bus system 16. It isalso possible that the analog-digital converter 14 is bodily and/orfunctionally integrated in the processing unit 15.

The processing unit 15 is joined to a communication means 17 of the bussystem 16, which puts the processed measured values on the transmissionpath of the bus system 16. The measured values are then transmitted viathe bus system 16 to a communication controller 18 assigned to thecontrol systems 19 according to a standard communication protocol ofprocess technology.

According to the invention, the entire functionality of the externalmeasuring and/or evaluating system 12 of the known sensor 1 and thecoupling 5 from FIG. 1 is relocated in the sensor 1 in FIG. 2 andimplemented there by the sensor electronics 3, the analog-digitalconverter 14, the processing unit 15 and/or the communication means 17.In particular, the functionality of transmitter, measured valuetransducer and/or converter is integrated into the processing unit 15and/or the communication means 17. All processing, calibration, sensordiagnostic, etc. takes place in the sensor 1 itself. The processed andprepared measured values are then directly transmitted to the controlsystem 19 and are used, shown or otherwise issued there for controllingor regulating a process. In the sensor according to the invention, nofurther manipulation of the sensor-measured values occurs outside of thesensor 1.

Due to the special design of the sensor 1 according to the invention,the use of the measuring and/or evaluating system 12 is no longerrequired. Instead, only a simpler and more economical analog-digitalconverter 14 is used. Additionally, according to the invention, onetransmission path of the known sensor 1 can be omitted, i.e., the pathwhich runs from the processing unit 8 to the measuring and/or evaluatingunit 12 and via which that data transmission occurs according to aproprietary protocol. Instead, in the sensor 1 according to theinvention, the digital measured values are transmitted directly to thecontrol system 19 via the bus system 16 by means of a typicalcommunication protocol of process technology.

In order to keep the costs of replacing sensors 1 from time to time aslow as possible, it is preferably provided to design the electronicsintegrated in the sensor 1 as an ASIC. In this manner, it is possible toimplement the sensor electronics 3, the analog-digital converter 14, theprocessing unit 15 (including periphery components) and thecommunication means 17 in one ASIC (so-called mixed mode with analog anddigital components in one ASIC). It is also possible to discretelyimplement the sensor electronics 3 conventionally and to only implementthe digital components, i.e., the analog-digital converter 14, theprocessing unit 15 and the communication means 17, on an ASIC. It iseven possible to implement the communication means 17 discretely, inparticular when this implements a data transmission according to theHART protocol. In the implementation of a data transmission according tothe protocol Profibus CA or the protocol Profibus DB it is more likely,for economical and spatial reasons at this point in time, to use ASICfor the implementation.

Additionally, the analog-digital converter 14 and the processing unit 15can be implemented in a first ASIC and the communication means 17 inanother ASIC. This implementation with a separate communication means 17could be practical, in particular for data transmission via the bussystem 16 according to the standard HART, the standard Profibus PA, thestandard Profibus DB or the standard Foundation Field Bus. Finally, itis also possible to implement only the processing unit 15 (includingperiphery components) on a first ASIC and the other components (sensorelectronics 3, analog-digital converter 14 and communication means 17)on another ASIC or on multiple further ASICs or on an FPGA or onmultiple further FPGAs or discretely. Should the individual componentsand circuit parts of the sensor be available more compact and economicalin the future that they can all be arranged without great expense in asensor housing 2, it is also possible to implement the sensorelectronics 3, the analog-digital converter 14, the processing unit 15and the communication means 17 of the sensor completely discretely,i.e., without an ASIC.

The electronics of the sensor 1 according to the invention can bedesigned in modules, wherein individual modules of the electronics canbe designed as FPGAs. The size of ASICs and/or FPGAs can be chosendepending on space available in the sensor housing 2. The dimensionscan, for example, be about 1.2 cm×2 cm, 1.5 cm×2.5 cm, 1 cm×5 cm or 1cm×10 cm, to name a few. The boards used for ASICs and/or FPGAs can bedesigned having multiple parts, wherein the individual board parts canbe moveably affixed to one another. To movably affix the individualboard parts, conductor paths formed on the printed circuit board orcorresponding foil conductors can be used, for example. Preferably, thepartial boards are galvanically decoupled from one another. However, itis possible that flexible printed circuit boards, e.g., foil conductorsare used and the boards for ASICs and/or FPGAs. In this manner, thespace inside of the sensor housing 2 can be used particularlyadvantageously.

In the sensor 1 according to the invention, the sensor housing 2 ispreferably formed as a hollow cylinder of plastic or stainless steel andpreferably has a diameter of 12 mm, so that the sensor 1 can beinstalled in standard facilities as are common in process technology.All of the electronics are designed in such a manner that they fit intoone sensor housing 2 with a diameter of 12 mm. This is advantageous inthat the same electronics can be installed in any sensor housing 2, i.e.in sensors having a diameter from 12 mm to 45 mm, in individual caseseven up to 100 mm.

The sensor according to the invention is preferably designed for use inareas at risk of explosion (ARTEX certification according to EN 50014,RiLi 94/9/EG and RiLi 1999/92/EG). Additionally, the sensor according tothe invention has high operation safety (fail safe) (SIL2 certificationaccording to EN 61508 and EN 61511). The SIL2 suitability of the sensor1 according to the invention requires a special circuit outlay. However,it is also possible to do without the SIL2 suitability of the sensor 1.

As already described further above, the sensors according to theinvention can be installed at operating temperatures from 65° C. to 130°C. and operating pressure from 6 bar to 8 bar.

What is claimed is:
 1. Sensor for at least one of liquid and gasanalysis, which is connectable directly to a higher-ranking controlsystem, comprising: a sensor housing, circuit means provided in saidsensor housing for collecting, processing and transmitting measuredvalues to said higher-ranking control system, wherein said circuit meanscomprises analog sensor electronics, an analog-digital converter forconverting detected analog measured values into digital measured values,a processing unit and communication means for processing andtransmitting said digital measured values to said higher-ranking controlsystem according to a communication protocol, and wherein means forgalvanic separation are provided at least one of between saidanalog-digital converter and said processing unit, and between saidprocessing unit and said communication means.
 2. Sensor according toclaim 1, wherein said analog sensor electronics allow for measuring oneof a pH-value, conductivity, oxygen content, chlorine content, ozonecontent, hydrogen peroxide content, free chlorine content, residualchlorine content, and turbidity and solids or gas content in a liquid.3. Sensor according to claim 1, wherein said communication means isadapted for transmitting said digital measured values to saidhigher-ranking control system according to one of the following fieldbus communication protocols: HART, Profibus PA, Profibus DP, andFoundation Field Bus, using two-wire technology.
 4. Sensor according toclaim 1, wherein said communication means is adapted for transmittingsaid digital measured values to said higher-ranking control systemaccording to one of the following communication standards: wirelessHART, WLAN, ZigBee, and RFID.
 5. Sensor according to claim 1, whereinsaid sensor housing is in the shape of a hollow cylinder having adiameter of 12 mm.
 6. Sensor according to claim 1, wherein said sensoris safe for use in areas at risk of at least one of explosion and fire.7. Sensor according to claim 1, wherein said sensor fulfills therequirements of standard SIL2.